JP7147478B2 - Nonaqueous electrolyte secondary battery and method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries, typified by lithium secondary batteries, have been used more and more in recent years, and there is a demand for the development of higher-capacity positive electrode materials.
Conventionally, as a positive electrode active material for non-aqueous electrolyte secondary batteries, a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure has been studied, and non-aqueous electrolyte secondary batteries using LiCoO ₂ have been widely put into practical use. there is The discharge capacity of LiCoO ₂ is about 120-130 mAh/g. Mn, which is abundant as an earth resource, is used as the transition metal (Me) constituting the lithium-transition metal composite oxide, and the molar ratio Li/Me of Li to the transition metal constituting the lithium-transition metal composite oxide is approximately 1. A non-aqueous electrolyte secondary battery using a so-called “LiMeO ₂ type” active material in which the Mn molar ratio Mn/Me in the transition metal is 0.5 or less has also been put to practical use. For example, LiNi _1/2 Mn _1/2 O ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ have a discharge capacity of 150 to 180 mAh/g.

On the other hand, in recent years, among lithium transition metal composite oxides having a α-NaFeO ₂ type crystal structure, the molar ratio Mn/Me of Mn in the transition metal (Me) has been increased, and the molar ratio of Li to the transition metal (Me) has been increased. A so-called “lithium-excessive” active material in which /Me exceeds 1 is known. When Li/Me is a certain size or more, this active material is charged within the potential range of 4.5 to 5.0 V (vs. Li/Li ⁺ ) in the initial charging process after assembling the battery. It is characterized by the observation of a region in which the potential change is relatively flat with respect to the amount of electricity. Even without it, it has a higher discharge capacity than the "LiMeO ₂ type" active material, so it is attracting attention (see Patent Document 1).

Patent Document 1 describes "an active material for a lithium secondary battery containing a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein the solid solution contains Li, Co, Ni and Mn. The composition ratio is Li 1 _{+ (1/3) x} Co _1-x-y Ni _{(1/2) y} Mn _{(2/3) x + (1/2) y} (x + y ≤ 1, 0 ≤ y, 1-x -y=z), and in the Li[Li _1/3 Mn _2/3 ]O ₂ (x)-LiNi _1/2 Mn _1/2 O ₂ (y)-LiCoO ₂ (z) system triangular phase diagram, (x, y, z) is point A (0.45, 0.55, 0), point B (0.63, 0.37, 0), point C (0.7, 0.25, 0 . 05), point D (0.67, 0.18, 0.15), point E (0.75, 0, 0.25), point F (0.55, 0, 0.45), and point G (0.45, 0.2, 0.35) represented by a range of values existing on or inside a heptagon ABCDEFG with vertices, and (003) plane and (104) plane by X-ray diffraction measurement The diffraction peak intensity ratio of is I ₍₀₀₃₎ /I ₍₁₀₄₎ ≧1.56 before charging and discharging, and I ₍₀₀₃₎ /I ₍₁₀₄₎ >1 at the end of discharging, and is 4.3 V (vs .Li/Li ⁺ ) to 4.8 V or less (vs. Li/Li ⁺ ), the step of performing initial charging to reach at least a region in which the potential change that appears with respect to the amount of charge electricity is relatively flat. An active material for a lithium secondary battery, characterized in that the amount of electricity that can be discharged in a potential region of 4.3 V (vs. Li/Li ⁺ ) or less is 177 mAh/g or more when passed through.” (Claim 3 ) in the positive electrode.

In addition, in paragraph [0058], "the active material for a lithium secondary battery according to the present invention is an active material existing in the region of x>1/3, and 2θ = A diffraction peak seen in Li[Li _1/3 Mn _2/3 ]O ₂ -type monoclinic crystals was observed around 20 to 30°, which indicates that Li ⁺ and Mn ⁴⁺ are in an ordered arrangement. It is estimated that it is a superlattice line observed when it is used." In order to manufacture a lithium secondary battery capable of extracting a sufficient discharge capacity even when a charging method is adopted in which the maximum potential of the positive electrode reaches 4.3 V (vs. Li/Li ⁺ ) or less, It is important to provide a charging process in consideration of the characteristic behavior of the active material for a lithium secondary battery according to the present invention, which will be described below, during the manufacturing process of the lithium secondary battery. When the active material for a secondary battery is used for the positive electrode and constant current charging is continued, a region in which the potential change is relatively flat is observed over a relatively long period of time in the positive electrode potential range of 4.3 V to 4.8 V. ^. However, this potential plateau region over a relatively long period is hardly observed when the value of x is less than 1/3, and conversely, when the value of x exceeds 2/3, Even when a relatively flat region of potential change is observed, it is short, and the conventional Li[Co _1-2x Ni _x Mn _x ]O ₂ (0≦x≦1/2)-based materials However, this behavior is not observed.This behavior is characteristic of the active material for a lithium secondary battery according to the present invention."

As an example of the lithium secondary battery, "lithium metal" is used for the negative electrode combined with the positive electrode, and "LiPF ₆ is used as the electrolyte in a mixed solvent with a volume ratio of EC/EMC/DMC of 6:7:7. 1 mol/l", and subjected to 5 cycles of initial charging/discharging process at 20°C. All voltage control was performed with respect to the positive electrode potential. A constant current constant voltage charge of 1 ItA and a voltage of 4.5 V was performed, and the charge termination condition was the time when the current value decreased to 1/6.Discharge was a constant current discharge of a current of 0.1 ItA and a final voltage of 2.0 V. A rest time of 30 minutes was set after charging and after discharging in all cycles.” (paragraphs [0112] to [0114]).

In addition, in Patent Document 2, "In a non-aqueous electrolyte secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte containing a non-aqueous solvent, the positive electrode active material is represented by the general formula (1) Li _1+x Mn _y M _z O ₂ (where x, y and z are 0<x<0.4, 0<y<1, 0<z<1 and x+y+z=1 wherein M is one or more metal elements and includes at least Ni or Co), and the non-aqueous solvent has two or more fluorine atoms directly bonded to the carbonate ring A non-aqueous electrolyte secondary battery comprising a fluorinated cyclic carbonate." (Claim 1).

Then, as Example 1 of the secondary battery, the positive electrode active material is "Li _1.2 Mn _0.54 Ni _0.13 Co _0.13 O ₂ ", the negative electrode contains silicon and carbon, and the non-aqueous electrolyte is "a non-aqueous solvent in which 4,5-difluoroethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 2:8, and LiPF ₆ is dissolved so as to be 1 mol/liter", and the initial charge is Discharge was performed by charging at a constant current of 0.5 It until the battery voltage reached 4.45 V, and then charging at a constant voltage of 4.45 V until the current value reached 0.05 It. The potential of the positive electrode was 4.60 V based on metallic lithium.Then, the battery was discharged at a constant current of 0.5 It until the battery voltage reached 1.50 V. [0049]).

Also known is a non-aqueous electrolyte secondary battery in which a lithium-excess active material is used for the positive electrode and a compound having an oxalate group bonded to boron is added to the non-aqueous electrolyte.
In Patent Document 3, "Lithium ion secondary having a positive electrode containing a positive electrode active material that operates at a potential of 4.4 V (vs Li/Li ⁺ ) or more, a negative electrode, and an electrolytic solution containing a non-aqueous solvent A battery, wherein the electrolytic solution contains 0.01% by mass or more and 10% by mass or less of a first lithium salt having a boron atom represented by the following formula (1) and / or formula (2), And a lithium ion secondary battery containing 1% by mass or more and 40% by mass or less of a second lithium salt that does not have a boron atom..." (Claim 1), "The first lithium salt is , LiBF ₄ , LiB(C ₂ O ₄ ) ₂ , and LiBF ₂ (C ₂ O ₄ ). battery." (Claim 4).

In paragraphs [0076] to [0083], as Example 1, the positive electrode active material is "0.5Li ₂ MnO ₃ -0.5LiNi _0.37 Mn _0.37 Co _0.26 O ₂ " and the negative electrode active material is graphite. The electrolytic solution is 9.8 g of a solution containing 1 mol/L of LiPF ₆ salt in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1:2 (...). A lithium ion secondary battery that is an "electrolytic solution A" in which 0.2 g of lithium bisoxaborate (... hereinafter referred to as "LiBOB") is mixed is described, paragraphs [0085] to [0087] In Example 3, a lithium ion secondary battery similar to that of Example 1 was produced except that the electrolyte solution C in which LiBOB in the electrolyte solution A of Example 1 was changed to LiBF ₂ (C ₂ O ₂ ) was used. Each battery was charged to 4.7 V and discharged to 2.0 V, and then charged to 4.5 V and discharged to 2.0 V for one cycle. It is described that the battery was evaluated by performing a 50-cycle charge/discharge test as discharge.

In Patent Document 4, "A lithium ion battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, the positive electrode active material contained in the positive electrode is the first charge when charging and discharging with metal Li as a counter electrode. The discharge efficiency is 80% to 90%, the negative electrode active material contained in the negative electrode is made of a mixed material of a silicon compound and a carbon material, and the negative electrode is doped with lithium for the irreversible capacity in the initial charge and discharge. A lithium ion battery, wherein the capacity ratio of the negative electrode to the positive electrode is 0.95 or more and 1 or less in the initial charging electric capacities of the positive electrode and the negative electrode.” (Claim 1) "The lithium ion battery according to claim 1, wherein the positive electrode active material is represented by the following chemical formula 1.
[Chemical Formula 1] aLi[Li1/3Mn2/ ₃ ] _O2・(1-a)Li[ _NixCoyMnz ] _O2 ( _0≤a≤0.3 , _0≤x≤1 , _0≤y ≤ 1, 0 ≤ z ≤ 1, x + y + z = 1)” (Claim 6), “The non-aqueous electrolytic solution comprises a solvent and a supporting salt, and the solvent is at least γ-butyrolactone (GBL), and the supporting electrolyte contains at least lithium bis(oxalate)borate (LiBOB).” (Claim 8) is described.

In paragraphs [0047] to [0054], as Example 1, the positive electrode active material is "(0.2Li ₂ MnO ₃ -0.8LiNi _0.33 Co _0.33 Mn _0.33 O ₂ ". , The negative electrode active material is a composite of “Si, SiO and HC”, and the non-aqueous electrolyte is “1M LiPF ₆ +0.05M LiBOB EC (ethylene carbonate):GBL (γ-butyrolactone) = 1:1 (vol% )”, and “the cutoff voltage for the initial charge and discharge is 2.2 to 4.6 V, the cutoff voltage for charge and discharge after the second cycle is 2.2 to 4.3 V, 60 A charge-discharge test was performed at ℃".

In Patent Document 5, "In a non-aqueous electrolyte secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte having lithium ion conductivity, the positive electrode active material is layered. having the general formula Li _1+x (N _a Mn _b Co _c )O _2+α (x+a+b+c=1, 0.7≦a+b, 0<x≦0.1, 0≦c/(a+b)<0.35, 0.7≦a/b≦2.0, −0.1≦α≦0.1), and the non-aqueous electrolyte contains lithium having an oxalate complex as an anion. A non-aqueous electrolyte secondary battery characterized by containing a salt” (Claim 1).

In paragraphs [0039] to [0058] and Table 1, as Examples 1 to 8, the positive electrode active materials are Li _1.06 Ni _0.47 Mn _0.47 O ₂ and Li _1.07 Ni _{0 .56} Mn _0.37 O ₂ or Li _1.07 Ni _0.42 Co _0.09 Mn _0.42 O ₂ , the negative electrode active material is graphite the surface of which is coated with amorphous carbon, and the electrolytic LiPF ₆ as a solute is dissolved in a mixed solvent of EC, MEC and DMC so that the liquid becomes 1 M, VC is added in an amount of 1% by weight, and lithium-bisoxalate borate ( LiBOB) was dissolved to a concentration of 0.1 M to prepare a non-aqueous electrolyte secondary battery. The battery was charged at a constant voltage of 2 V to 50 mA, discharged at 330 mA to 2.4 V, and the capacity at this time was taken as the battery discharge capacity” (paragraph [0045]). It states that it was measured.

In Patent Document 6, as Example 22, the positive electrode active material is "lithium manganate (Li _1.1 Mn _1.9 Al _0.1 O ₄ , LMO) 80% by mass and Li _1.15 Ni _0.45 Mn _0.45 Co _0.10 O ₂ (Co-less LNMC) 20% by mass” (paragraph [0401]), the negative electrode active material is “artificial graphite powder” (paragraph [0343]), and the non-aqueous electrolyte "Mixed ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (30:30:40 by volume), then added 0.1 mol/L of sufficiently dried LiFSO ₃ and added lithium Lithium obtained by dissolving bisoxalate borate (LiB(C ₂ O ₄ ) ₂ , LiBOB) at a ratio of 0.1 mol/L and LiPF ₆ at a ratio of 1 mol/L (paragraph [0408]) A secondary battery is described.

Then, regarding the evaluation of the initial discharge capacity of the lithium secondary battery according to Example 22, "the lithium secondary battery was sandwiched between glass plates in order to improve the adhesion between the electrodes, and at 25 ° C., 0.1 C After charging to 4.2 V at a constant current corresponding to , discharging to 3.0 V at a constant current of 0.1 C. In the second and third cycles, after charging to 4.2 V at 0.33 C, 4.2 V The battery was charged until the current value reached 0.05 C at a constant voltage of , discharged to 3.0 V at a constant current of 0.33 C, and the initial discharge capacity was obtained from the third cycle discharge process.” (Paragraph [ 0404]), and regarding the evaluation of the high-temperature storage characteristics of the same battery, the remaining capacity after storage at 75 ° C., the recovery capacity after storage at 75 ° C., and the storage capacity retention rate were measured by constant current charging up to 4.2 V and 4 It is described that evaluation was performed with a constant voltage charge of .2V.

Japanese Patent No. 4877660 JP 2012-104335 A JP 2013-191390 A JP 2016-100054 A JP 2010-050079 A JP 2011-187440 A

Non-aqueous electrolyte secondary batteries are required by the standards ( For example, it is defined by "GB/T (Recommended National Standard of China)" for automobile batteries. As a method to evaluate whether the safety has been improved, assuming that the charging control circuit is broken, when the current is forcibly applied beyond the fully charged state, a sudden increase in the battery voltage is observed SOC is there a way to record Safety is evaluated as improved when no rapid increase in battery voltage is observed up to higher SOC.
Here, SOC is an abbreviation for State Of Charge, and represents the state of charge of the battery by the ratio of the remaining capacity at that time to the capacity at full charge, and the fully charged state is expressed as "SOC 100%". .

In Patent Documents 1 to 4, it is assumed that a lithium-excess type active material is used for the positive electrode, and that the positive electrode potential is manufactured through an initial charge/discharge process until the positive electrode potential reaches 4.5 V (vs. Li/Li ⁺ ) or more. However, there is no mention of delaying the rapid increase in battery voltage to a higher SOC when the non-aqueous electrolyte secondary battery is overcharged.
On the other hand, in Patent Documents 5 and 6, a lithium-excess type active material having a Li/Me ratio of 1 or more is used for the positive electrode, and the initial charge/discharge process is performed at a voltage of 4.2 V (the positive electrode potential is about 4.3 V (vs. Li/Li A non-aqueous electrolyte secondary battery is described which is considered to be ⁺ ). However, the lithium-excess type active materials according to the examples described in Patent Documents 5 and 6 have a small Li/Me ratio of 1.15 or less. In addition, in Patent Document 1, in the case of a lithium-excess type active material existing in the region of x>1/3 (Li/Me>1.25), "2θ of X-ray diffraction diagram using CuKα rays = 20 A diffraction peak seen in a Li[Li _1/3 Mn _2/3 ]O ₂ type monoclinic crystal is observed near ~ 30 °.” In the lithium-excess type active material described in Patent Documents 5 and 6, even if the maximum potential of the positive electrode in the initial charge/discharge process is less than 4.5 V (vs. Li/Li ⁺ ), 2θ = 20 ~ There is a high probability that no diffraction peak will be observed in the 22° range. Patent Documents 5 and 6 also do not disclose delaying the rapid increase in battery voltage to a higher SOC when the non-aqueous electrolyte secondary battery is overcharged.

An object of the present invention is to provide a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to higher SOC.

One aspect of the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ type crystal structure as an active material and has the general formula Li _1+α Me _1-α O ₂ (0<α, Me is a transition metal element containing Ni and Mn, or Ni, Mn and Co), and the active material uses CuKα rays. This is a non-aqueous electrolyte secondary battery in which a diffraction peak is observed in the range of 20 to 22° in the X-ray diffraction pattern obtained.

Another aspect of the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ -type crystal structure as an active material and has the general formula Li _1+α A lithium-transition metal composite oxide represented by Me _1-α O ₂ (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co), and the positive electrode has a positive electrode potential of 5 When charging up to .0V (vs. Li/Li ⁺ ), the potential change is compared with the amount of charge in the positive electrode potential range of 4.5 to 5.0 V (vs. Li/Li ⁺ ). This is a non-aqueous electrolyte secondary battery in which a relatively flat region is observed.

Still another aspect of the present invention is the method for manufacturing the non-aqueous electrolyte secondary battery, wherein the maximum potential of the positive electrode in the initial charge and discharge process is less than 4.5 V (vs. Li/Li ⁺ ). A method for manufacturing a water electrolyte secondary battery.

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery in which a sudden rise in battery voltage is not observed up to a higher SOC, and a method for manufacturing the same.

1 is an X-ray diffraction diagram of a positive electrode active material included in a non-aqueous electrolyte secondary battery according to an embodiment of the present invention and a non-aqueous electrolyte secondary battery according to a conventional example; FIG. 10 is a graph showing changes in positive electrode potential with respect to charged electricity observed when positive electrodes containing LiMeO ₂ type and lithium-excess active materials are initially charged with the positive electrode charge upper limit potential of 4.6 V (vs. Li/Li ⁺ ). FIG. 4 is a diagram for explaining “a region in which the potential change is relatively flat with respect to the amount of charged electricity” in the non-aqueous electrolyte secondary battery according to the embodiment of the present invention; 1 is a perspective view showing an embodiment of a non-aqueous electrolyte secondary battery according to one aspect of the present invention; FIG. Schematic diagram showing a power storage device including a plurality of nonaqueous electrolyte secondary batteries according to one embodiment of the present invention

The configuration and effects of the present invention will be described with technical ideas. However, the mechanism of action is presumed, and whether it is correct or not does not limit the present invention. In addition, the present invention can be embodied in various other forms without departing from its spirit or essential characteristics. Therefore, the embodiments or examples described below are merely illustrative in every respect and should not be construed as limiting. Furthermore, all modifications and changes that fall within the equivalent scope of claims are within the scope of the present invention.

One embodiment of the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ -type crystal structure as an active material and has the general formula Li _1+α A lithium transition metal composite oxide represented by Me _1-α O ₂ (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co), and the active material emits CuKα rays. It is a non-aqueous electrolyte secondary battery in which a diffraction peak is observed in the range of 20 to 22° in the X-ray diffraction diagram used.

Another embodiment of the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ type crystal structure as an active material and has the general formula Li _1+α Me _1-α O ₂ (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co), and the positive electrode has a positive electrode potential is charged to 5.0 V (vs. Li/Li ⁺ ), the potential change with respect to the charged quantity of electricity within the positive electrode potential range of 4.5 to 5.0 V (vs. Li/Li ⁺ ) is a non-aqueous electrolyte secondary battery having a positive electrode in which a relatively flat region is observed.

In the non-aqueous electrolyte secondary battery, a lithium-transition metal composite oxide having a molar ratio of Mn to transition metal (Me) of 0.4≦Mn/Me may be used as the positive electrode active material. According to this aspect, the layered structure of the active material can be stabilized.

In the non-aqueous electrolyte secondary battery, a lithium-transition metal composite oxide having a molar ratio of Li to transition metal (Me) of 1.15<Li/Me may be used as the positive electrode active material.
According to this aspect, it is possible to provide a non-aqueous electrolyte secondary battery in which no sudden increase in battery voltage is observed up to a higher SOC.

In the non-aqueous electrolyte secondary battery, the positive electrode active material may be a lithium-transition metal composite oxide in which the molar ratio of Li to transition metal (Me) is Li/Me≦1.35. According to this aspect, the discharge capacity can be improved.

The non-aqueous electrolyte secondary battery is preferably used at a battery voltage at which the maximum potential of the positive electrode in a fully charged state (SOC 100%) is less than 4.5 V (vs. Li/Li ⁺ ).

According to the above embodiments, it is possible to provide a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC.

In the non-aqueous electrolyte secondary battery, a non-aqueous electrolyte containing a fluorinated cyclic carbonate as a non-aqueous solvent may be used as the non-aqueous electrolyte. According to such a configuration, in addition to the effect that it is possible to provide a non-aqueous electrolyte secondary battery in which a sudden increase in battery voltage is not observed up to a higher SOC, an increase in AC resistance after storage is suppressed. There is an effect that it can be done.

The non-aqueous electrolyte may contain a compound having an oxalate group bonded to boron.
According to this aspect, in addition to the effect of being able to provide a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC, the effect of being able to reduce the initial AC resistance is obtained. played.

Still another embodiment of the present invention is the method for manufacturing the non-aqueous electrolyte secondary battery, wherein the maximum potential of the positive electrode in the initial charge/discharge step is less than 4.5 V (vs. Li/Li ⁺ ). , a method for manufacturing a non-aqueous electrolyte secondary battery.
In this specification, the term “initial” charging and discharging refers to one or more charging and discharging operations performed after injecting the non-aqueous electrolyte. Refers to the first charging and discharging after injection.
According to this embodiment, a non-aqueous electrolyte secondary battery is manufactured in which no rapid increase in battery voltage is observed up to higher SOC.
One embodiment of the present invention described above, another embodiment of the present invention, and still another embodiment of the present invention will be described in detail below.

<Lithium transition metal composite oxide>
Lithium transition metal contained as an active material in the positive electrode included in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention and another embodiment of the present invention (hereinafter collectively referred to as "this embodiment") The composite oxide is a so-called “lithium-excess type” active material represented by the general formula Li _1+α Me _1-α O ₂ (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co). is. Typically, it can be expressed as Li _1+α (Ni _β Co _γ Mn _δ ) _1-α O ₂ (β+γ+δ=1). In order to provide a positive electrode active material that can be used as a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC, the molar ratio of Li to the transition metal element Me, Li/Me, that is, (1+α) /(1-α) is preferably greater than 1.15, more preferably 1.2 or greater, and even more preferably 1.23 or greater. In order to obtain excellent discharge capacity, Li/Me is preferably 1.35 or less, more preferably 1.3 or less.
From the viewpoint of stabilizing the layered structure, the molar ratio Mn/Me of Mn to the transition metal element Me, that is, δ, is preferably 0.4 or more, more preferably 0.45 or more. Moreover, from the viewpoint of charge/discharge capacity, Mn/Me is preferably 0.65 or less, more preferably 0.60 or less.
The molar ratio Ni/Me of Ni to the transition metal element Me, that is, β, is preferably 0.2 or more in order to improve the charge/discharge cycle performance of the non-aqueous electrolyte secondary battery. Also, it is preferably 0.5 or less, more preferably 0.4 or less.
The molar ratio Co/Me of Co to the transition metal element Me, that is, γ, is preferably 0.0 or more, more preferably 0.2 or more, from the viewpoint of increasing the conductivity of the active material particles. In order to reduce material costs, it is preferably 0.4 or less, more preferably 0.3 or less.
In addition, the lithium-transition metal composite oxide according to the present embodiment contains alkali metals such as Na and K, alkaline earth metals such as Mg and Ca, and 3d transition metals such as Fe within a range that does not impair the effects of the present invention. It does not exclude the inclusion of minor amounts of other metals, such as the transition metals represented.

The lithium-transition metal composite oxide according to this embodiment has an α-NaFeO ₂ type crystal structure. The lithium transition metal composite oxide after synthesis (before charging and discharging) belongs to the space group P3 ₁ 12, and in an X-ray diffraction diagram using CuKα rays, a superlattice peak in the range of 2θ = 20 to 22 °. (Peak observed in Li[Li _1/3 Mn _2/3 ]O ₂ -type monoclinic crystal) is observed. This superlattice peak (hereinafter referred to as “diffraction peak in the range of 20 to 22°”) disappears even when charging and discharging is performed in a potential region where the positive electrode potential is less than 4.5 V (vs. Li/Li ⁺ ). I have nothing to do. However, once the charge is performed to a potential of 4.5 V (vs. Li/Li ⁺ ) or more, the symmetry of the crystal changes due to the detachment of Li from the crystal, resulting in a 20 to 22° angle. The range of diffraction peaks disappears, and the lithium-transition metal composite oxide belongs to the space group R3-m. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and when the atomic arrangement in R3-m is ordered, the P3 ₁ 12 model is adopted. Note that "R3-m" is originally written by adding a bar "-" above the "3" of "R3m".

<Positive electrode active material>
The positive electrode active material of the non-aqueous electrolyte secondary battery according to the present embodiment contains the lithium transition metal composite oxide, and when X-ray diffraction measurement is performed using CuKα rays, the X-ray diffraction diagram shows that the It has the feature that a diffraction peak is observed in the range.

<Confirmation method of diffraction peak>
The positive electrode active material used in the non-aqueous electrolyte secondary battery according to the present embodiment and the positive electrode active material contained in the positive electrode included in the non-aqueous electrolyte secondary battery according to the present embodiment were subjected to X-ray diffraction measurement, and CuKα rays were used. Confirmation that a diffraction peak is observed in the range of 20 to 22° in the X-ray diffraction diagram is performed by the following procedures and conditions. Here, “observed” means the maximum intensity within the range of diffraction angles of 20 to 22° with respect to the difference (I ₁₈ ) between the maximum and minimum values of intensity within the range of diffraction angles of 17 to 19°. and the minimum value (I ₂₁ ), that is, the value of “I ₂₁ /I ₁₈ ” is in the range of 0.001 to 0.1.
If the sample to be subjected to the X-ray diffraction measurement is the active material powder (powder before charging/discharging) before manufacturing the positive electrode, it is directly subjected to the measurement. When collecting a sample from a positive electrode taken out after disassembling a non-aqueous electrolyte secondary battery (hereinafter also referred to as "battery"), before disassembling the battery, 10 minutes of the nominal capacity (Ah) of the battery At a current value (A) of 1, constant current discharge is performed until the battery voltage reaches the lower limit of the specified voltage, and the battery is in a completely discharged state. As a result of dismantling, if the battery uses a metal lithium electrode as the negative electrode, the positive electrode is taken out without performing the additional work described below. If the battery does not use a metallic lithium electrode as the negative electrode, in order to accurately control the positive electrode potential, as an additional task, disassemble the battery, remove the positive electrode, and then assemble a test battery with a metallic lithium electrode as the counter electrode. Constant current discharge is performed at a current value of 10 mA per 1 g of the mixture until the positive electrode potential reaches 2.0 V (vs. Li/Li ⁺ ), adjusted to a completely discharged state, dismantled again, and the positive electrode is taken out.
The removed positive electrode is thoroughly washed with dimethyl carbonate to remove the non-aqueous electrolyte adhering to the positive electrode, dried at room temperature for a whole day and night, and then the positive electrode mixture is collected from the current collector. The collected positive electrode mixture is lightly pulverized in an agate mortar, placed on a sample holder for X-ray diffraction measurement, and subjected to measurement.
The operations from dismantling to re-dismantling of the battery, cleaning and drying of the positive electrode are performed in an argon atmosphere with a dew point of -60°C or lower.

<X-ray diffraction measurement>
In this specification, the X-ray diffraction measurement is performed under the following conditions. The radiation source is CuKα, the acceleration voltage is 30 kV, and the acceleration current is 15 mA. The sampling width is 0.01 deg, the scanning speed is 1.0 deg/min, the divergence slit width is 0.625 deg, the light receiving slit is open, and the scattering slit width is 8.0 mm.

As shown in Example 1 to be described later, after assembling a non-aqueous electrolyte secondary battery using a lithium-excess type active material as a positive electrode and metallic lithium as a negative electrode, the upper limit charging potential is set to 4.25 V (vs. Li/Li ⁺ ). , with a lower discharge potential of 2.0 V (vs. Li/Li ⁺ ), and a current value equivalent to 0.1 C, the fully discharged non-aqueous electrolyte secondary battery was dismantled after being charged and discharged twice. When the positive electrode thus obtained is subjected to X-ray diffraction measurement according to the procedure described above, an X-ray diffraction pattern in which a diffraction peak is observed in the range of 20 to 22° is obtained as in the lower part of FIG.
Further, as shown in Comparative Example 2 to be described later, after assembling a non-aqueous electrolyte secondary battery using a lithium-excess type active material as a positive electrode and metallic lithium as a negative electrode, the upper limit charging potential is set to 4.6 V (vs. Li/Li ⁺ ), the lower limit of discharge potential was set to 2.0 V (vs. Li ^/ Li ⁺ ), and the initial charge and discharge was performed. Then, the upper limit of charge potential was set to 4.25 V (vs. Positive electrode obtained by dismantling a completely discharged non-aqueous electrolyte secondary battery completed by performing a second charge/discharge (current value equivalent to 0.1 C in both cases) at 0 V (vs. Li/Li ⁺ ) When the X-ray diffraction measurement is performed according to the procedure described above, an X-ray diffraction diagram is obtained in which no peak in the range of 20° to 22° is observed, as in the upper part of FIG. That is, as described above, once the battery is charged to a potential of 4.5 V (vs. Li/Li ⁺ ) or higher, no peak in the range of 20 to 22° is observed.
In the non-aqueous electrolyte secondary battery according to the present embodiment, even after charging and discharging, a diffraction peak in the range of 20 to 22 ° is observed in the X-ray diffraction diagram of the positive electrode active material measured by the above procedure. In the non-aqueous electrolyte secondary battery according to the embodiment, the maximum potential of the positive electrode in a fully charged state (SOC 100%) is less than 4.5 V (vs. Li/Li ⁺ ) including initial charge and discharge. known to be used.

In addition, when the non-aqueous electrolyte secondary battery according to the present embodiment is charged to a positive electrode potential of 5.0 V (vs. Li/Li ⁺ ), it is 4.5 to 5.0 V (vs. Li/Li ⁺ ), a region in which the potential change is relatively flat with respect to the amount of charged electricity (hereinafter also referred to as “flat potential change region”) is observed. In addition, if charging is performed even once until the charging process in which the flat potential change is observed is completed, then charging is performed until the positive electrode potential reaches 5.0 V (vs. Li/Li ⁺ ). However, the flat regions above the potential change are not observed again.

The principle of the working mechanism of the present invention will be described with reference to FIG. The solid line in FIG. 2 indicates the non-aqueous electrolyte 2 according to the present embodiment, which includes a positive electrode using a lithium transition metal composite oxide (denoted as “excess lithium type”) as a positive electrode active material and a negative electrode using metallic lithium. The change in the positive electrode potential is shown when the following battery is assembled and the initial charge is performed with the upper limit charging potential of the positive electrode set to 4.6 V (vs. Li/Li ⁺ ). The dashed line indicates a non-aqueous non-aqueous electrode having the same configuration except that it has a positive electrode using commercially available LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (denoted as “LiMeO ₂ type”) as a positive electrode active material. It shows the change in the positive electrode potential when the electrolyte secondary battery is similarly charged for the first time. In the positive electrode using the lithium-excess active material, a flat potential change region is observed within the positive electrode potential range of 4.45 to 4.6 V (vs. Li/Li ⁺ ). On the other hand, in the positive electrode using the LiMeO ₂ -type active material, no flat potential change region is observed within the positive electrode potential range of 4.45 to 4.6 V (vs. Li/Li ⁺ ).
Note that the potential range in which a flat region is observed and the capacity during charge/discharge slightly vary depending on physical properties such as composition even for positive electrodes using a lithium-excess type active material, so this figure is only an example.

In the non-aqueous electrolyte secondary battery according to the present embodiment, when the positive electrode potential is charged to 5.0 V (vs. Li/Li ⁺ ), a region where the potential change is flat is observed. Excessive lithium active material is included in the positive electrode, but in the initial charge/discharge process, the battery is completed without charging until the end of the charging process in which the flat region is observed. The maximum potential of the positive electrode in the initial charging/discharging step is preferably less than 4.5 V (vs. Li/Li ⁺ ). Furthermore, the non-aqueous electrolyte secondary battery according to the present embodiment is used under charging conditions in which charging is not performed until the charging process in which the flat region is observed is completed. Therefore, in the non-aqueous electrolyte secondary battery according to the present embodiment, from the manufacturing stage to the time of use, charging is not performed even once until the charging process in which the flat region is observed is completed. In this case, a region in which the potential change is flat with respect to the charge quantity of electricity is observed within the positive electrode potential range of 4.5 to 5.0 V (vs. Li/Li ⁺ ).
By utilizing the behavior described above, the non-aqueous electrolyte secondary battery according to the present embodiment can reach a higher SOC even if it is overcharged beyond 100% SOC, which is the fully charged state during normal use. A sudden rise in the battery voltage (positive electrode potential) can be suppressed.

<Method for confirming the area where the potential change is flat>
Here, the following procedure is used to confirm that the "area where the potential change is flat" is observed. A non-aqueous electrolyte secondary battery is disassembled and taken out to prepare a test battery using the positive electrode as the working electrode and metal lithium as the counter electrode. Since the battery voltage and the working electrode potential (positive electrode potential) of the test battery are substantially the same value, the positive electrode potential in the following procedure can be read as the battery voltage of the test battery. The test battery is discharged at a current value of 10 mA per 1 g of the positive electrode mixture until the final potential of the positive electrode is 2.0 V (vs. Li/Li ⁺ ), and then rested for 30 minutes. After that, constant current charging is performed at a current value of 10 mA per 1 g of the positive electrode mixture until the final potential of the positive electrode is 5.0 V (vs. Li/Li ⁺ ). Here, when the capacity when reaching 4.45 V (vs. Li/Li ⁺ ) from the start of charging is X (mAh) and the capacity at each potential is Y (mAh), Y/X*100 is the capacity ratio Z (%). A dZ/dV curve can be obtained by plotting dZ/dV with the positive electrode potential on the horizontal axis, the difference in potential change on the denominator on the vertical axis, and the difference in capacitance ratio change on the numerator.
A solid line in FIG. ⁺ ) is an example of a dZ/dV curve when charging is performed. As can be seen from the formula for the dZ/dV curve, when the potential change is small with respect to the capacitance ratio change, the dZ/dV value is large, and when the potential change is large with respect to the capacitance ratio change, the dZ/dV value is value becomes smaller. In the charging process of the lithium-excess type active material, the value of dZ/dV becomes large in the region where the potential change is flat in the potential region exceeding 4.5 V (vs. Li/Li ⁺ ). After that, when the region where the potential change is flat ends and the potential starts to rise again, the value of dZ/dV becomes smaller. That is, a peak is observed in the dZ/dV curve. Here, when the maximum value of dZ/dV in the range of 4.5 V (vs. Li/Li ⁺ ) to 5.0 V (vs. Li/Li ⁺ ) is 150 or more, the potential change with respect to the amount of charge determines that a flat region is observed. On the other hand, the dashed line is the dZ/dV curve of a battery having the same configuration except that it has a positive electrode using a commercially available LiMeO ₂ type active material as a positive electrode active material and subjected to the same test. A peak such as that seen in the lithium-excess type is not observed, corresponding to the fact that no flat region of potential change is observed. In this specification, the term "during normal use" refers to the case where the non-aqueous electrolyte secondary battery is used under the charging and discharging conditions recommended or specified for the non-aqueous electrolyte secondary battery. When a charger for the non-aqueous electrolyte secondary battery is prepared, it refers to the case where the non-aqueous electrolyte secondary battery is used by applying the charger.

<Method for Producing Precursor of Lithium Transition Metal Composite Oxide>
Next, a method for producing the precursor of the lithium-transition metal composite oxide used for producing the positive electrode active material of the non-aqueous electrolyte secondary battery according to this embodiment will be described.
The lithium-transition metal composite oxide according to the present embodiment is basically a raw material containing metal elements (Li, Ni, Co and Mn) constituting the active material according to the composition of the target active material (oxide). can be obtained by preparing and firing this.
In producing a composite oxide with the desired composition, the so-called "solid phase method" in which compounds of Li, Ni, Co and Mn are mixed and fired, or Ni, Co and Mn are pre-existed in one particle. A "coprecipitation method" is known in which a coprecipitate precursor is prepared and then mixed with a lithium salt and fired. In the synthesis process by the "solid-phase method", it is difficult to obtain a sample in which each element is uniformly distributed in one particle, especially since Mn is difficult to form a uniform solid solution with Ni and Co. Until now, many attempts have been made in the literature to form a solid solution of Mn (LiNi _1-x Mn _x O ₂ , etc.) in part of Ni or Co by a solid-phase method, but the “coprecipitation method” was selected. It is easier to obtain a homogeneous phase at the atomic level. Therefore, the "coprecipitation method" is employed in the method for producing the precursor of the lithium-transition metal composite oxide according to the present embodiment.

In the method for producing a precursor of a lithium-transition metal composite oxide according to the present embodiment, a raw material aqueous solution containing Ni, Co, and Mn is added dropwise, and a compound containing Ni, Co, and Mn is coprecipitated in the solution. It is preferable to prepare the precursor by
In producing the coprecipitated precursor, Mn among Ni, Co and Mn is easily oxidized, and it is not easy to produce a coprecipitated precursor in which Ni, Co and Mn are uniformly distributed in a divalent state. , Ni, Co and Mn at the atomic level tend to be insufficient. Therefore, in the present invention, it is preferable to remove dissolved oxygen in order to suppress the oxidation of Mn distributed in the coprecipitate precursor. A method of removing dissolved oxygen includes a method of bubbling an oxygen-free gas. As the gas that does not contain oxygen (O ₂ ), nitrogen gas, argon gas, carbon dioxide (CO ₂ ), etc. can be used, although not limited thereto.

The pH in the step of co-precipitating a compound containing Ni, Co and Mn in a solution to produce a precursor is not limited, but the co-precipitated precursor is produced as a co-precipitated hydroxide precursor. If so, it can be 10.5 to 14. It is preferable to control the pH in order to increase the tap density of the precursor and composite oxide. By setting the pH to 11.5 or less, the composite oxide can have a tap density of 1.00 g/cm ³ or more, and high rate discharge performance can be improved. Furthermore, by setting the pH to 11.0 or less, particle growth can be promoted, so that the duration of stirring after the end of dropping the raw material aqueous solution can be shortened.
Further, when the coprecipitate precursor is to be produced as a coprecipitate carbonate precursor, the pH can be adjusted to 7.5-11. By setting the pH to 9.4 or less, the composite oxide can have a tap density of 1.25 g/cm ³ or more, and high rate discharge performance can be improved. Furthermore, by setting the pH to 8.0 or less, particle growth can be promoted, so that the duration of stirring after the end of dropping the raw material aqueous solution can be shortened.

Raw materials for the coprecipitate precursor include Ni sources such as nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate, etc., and Co sources such as cobalt sulfate, cobalt nitrate, cobalt acetate, etc., and Mn sources. Examples thereof include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, and manganese acetate.

The dropping speed of the raw material aqueous solution greatly affects the uniformity of the elemental distribution within one particle of the coprecipitate precursor to be produced. A preferable dropping rate is preferably 30 mL/min or less, although it is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, and the like. In order to improve the discharge capacity, the dropping rate is more preferably 10 mL/min or less, most preferably 5 mL/min or less.

_In addition, when a complexing agent such as NH is present in the reaction tank and a constant convection condition is applied, by continuing stirring after the dropping of the raw material aqueous solution, the rotation of the particles and the Revolution is accelerated, and in this process, the particles gradually grow into concentric spheres while colliding with each other. That is, the coprecipitate precursor undergoes a two-stage reaction: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction vessel, and a precipitate formation reaction that occurs while the metal complex stays in the reaction vessel. It is formed. Therefore, the coprecipitate precursor having the desired particle size can be obtained by appropriately selecting the time for continuing the stirring after the dropping of the raw material aqueous solution.

Regarding the preferable duration of stirring after the completion of dropping the raw material aqueous solution, it is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but it is 0.5 hours or more in order to grow the particles as uniform spherical particles. is preferred, and 1 hour or more is more preferred. In addition, in order to reduce the possibility that the output performance of the battery in the low SOC region will be insufficient due to an excessively large particle size, the time is preferably 30 hours or less, more preferably 25 hours or less, and most preferably 20 hours or less.

<Method for Producing Lithium Transition Metal Composite Oxide>
The method for producing the positive electrode active material of the non-aqueous electrolyte secondary battery according to the present embodiment is preferably a method of mixing the coprecipitate precursor and the lithium compound and calcining the mixture.
Examples of the lithium compound include lithium hydroxide and lithium carbonate. As for the total amount of the lithium compound, it is preferable to add an excess amount of about 1 to 5 mol % in anticipation of part of the lithium compound being lost during firing.
In addition to these lithium compounds, lithium fluoride, lithium sulfate, or lithium phosphate may be used as a sintering aid. The addition ratio of these sintering aids is preferably 1 to 10 mol % with respect to the total molar amount of the lithium compound.

The firing temperature affects the charge-discharge cycle performance of the positive electrode active material.
If the firing temperature is too low, crystallization will not proceed sufficiently, and charge/discharge cycle performance will tend to deteriorate. In one aspect of the present invention, the firing temperature is preferably 800° C. or higher. When the temperature is 800° C. or higher, active material particles having a high degree of crystallinity can be obtained, and charge/discharge cycle performance can be improved.

On the other hand, if the sintering temperature is too high, the structure changes from the layered α-NaFeO ₂ structure to the rocksalt cubic crystal structure, which is disadvantageous to the movement of lithium ions in the active material during the charge-discharge reaction, resulting in poor charge-discharge cycle performance. descend. In the present invention, the firing temperature is preferably 1000° C. or less. By setting the temperature to 1000° C. or less, it is possible to obtain active material particles in which structural change to a rock salt-type cubic crystal structure is suppressed, and to improve charge-discharge cycle performance.
Therefore, when producing a positive electrode active material containing a lithium-transition metal composite oxide according to one aspect of the present invention, the firing temperature is preferably 800 to 1000° C. in order to improve charge-discharge cycle performance.

The surface of the primary particles and/or secondary particles of the lithium-transition metal composite oxide obtained by firing is coated with a different element in order to obtain a positive electrode active material with a high energy density retention rate and improved coulombic efficiency. and/or may be dissolved. Examples of foreign elements include aluminum compounds.
In order to coat the aluminum compound, a method of putting the synthesized lithium-transition metal composite oxide particles into an aqueous solution of a compound containing aluminum (sulfate, nitrate, acetate, etc.) can be adopted. This aqueous solution is preferably acidic. However, the order of charging is not limited to this. For example, a method of adding an aqueous solution of a compound containing aluminum to lithium-transition metal composite oxide particles dispersed in water may be employed. Further, a pH adjuster may be added after or during the addition of the lithium-transition metal composite oxide to the aluminum-containing aqueous solution. The pH adjuster is not limited as long as it is an alkaline solution. Examples of the alkaline solution include NaOH aqueous solution and KOH aqueous solution. The pH value adjusted by adding the pH adjuster can be selected as appropriate.
The particles to which the aluminum compound has been added are separated by filtration or the like, and the obtained particles are preferably dried at 80 to 120° C. and further heat-treated in the air at 300 to 500° C. for 1 to 10 hours. By performing the above, lithium-transition metal composite oxide particles having aluminum-containing oxides present on the particle surfaces can be obtained.
When coating the surface of the lithium-transition metal composite oxide particles with the aluminum compound, the aluminum compound is preferably 0.1% by mass to 0.7% by mass with respect to the lithium-transition metal composite oxide, More preferably, when the content is 0.2% by mass to 0.6% by mass, the effect of further improving the energy density retention rate and the effect of improving the coulombic efficiency are more fully exhibited.

<Negative electrode material>
The negative electrode material of the battery according to the present embodiment is not limited, and any material can be selected as long as it can release or absorb lithium ions. For example, lithium composite oxides such as lithium titanate having a spinel crystal structure represented by Li[Li _1/3 Ti _5/3 ]O ₄ , metallic lithium, lithium alloys (lithium-silicon, lithium-aluminum, lithium - metallic lithium-containing alloys such as lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and Wood's alloys), silicon capable of storing and releasing lithium, metals such as antimony and tin, alloys thereof, silicon oxide , metal oxides such as tin oxide, carbon materials (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.), and the like.

<Positive electrode/negative electrode>
The positive electrode active material and the negative electrode material are preferably powders with an average particle size of 100 μm or less. In particular, the powder of the positive electrode active material is preferably 15 μm or less in order to improve the high output characteristics of the non-aqueous electrolyte secondary battery, and preferably 10 μm or more in order to maintain charge-discharge cycle performance. . A pulverizer or a classifier is used to obtain powder in a predetermined shape. For pulverization, for example, a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter jet mill, whirling jet mill, sieve and the like are used. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane is allowed to coexist can also be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like may be used as necessary, both dry and wet.

The positive electrode active material and the negative electrode material, which are the main constituent components of the positive electrode and the negative electrode, have been described in detail above. etc. may be contained as other constituents.

The conductive agent is not limited as long as it is an electronically conductive material that does not adversely affect the battery performance. Conductive materials such as ketjen black, carbon whiskers, carbon fibers, metal (copper, nickel, aluminum, silver, gold, etc.) powders, metal fibers, and conductive ceramics materials can be included singly or as a mixture thereof. .

Among these, acetylene black is preferable as the conductive agent from the viewpoint of electronic conductivity and coatability. The amount of the conductive agent added is preferably 0.1% by mass to 50% by mass, particularly preferably 0.5% by mass to 30% by mass, based on the total mass of the positive electrode or negative electrode. In particular, it is preferable to grind acetylene black into ultrafine particles of 0.1 to 0.5 μm and use it, because the required amount of carbon can be reduced. These mixing methods are physical mixing, the ideal of which is homogeneous mixing. Therefore, dry or wet mixing can be performed using a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, or a planetary ball mill.

The binders are generally polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), thermoplastic resins such as polyethylene and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene butadiene. A polymer having rubber elasticity such as rubber (SBR) and fluororubber can be used singly or as a mixture of two or more. The amount of the binder added is preferably 1 to 50% by mass, particularly preferably 2 to 30% by mass, based on the total mass of the positive electrode or negative electrode.

The filler is not limited as long as it is a material that does not adversely affect battery performance. Ordinarily, olefinic polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The amount of filler added is preferably 30% by mass or less with respect to the total mass of the positive electrode or negative electrode.

The positive electrode and the negative electrode are obtained after mixing the main constituent components (positive electrode active material for the positive electrode, negative electrode material for the negative electrode) and other materials in an organic solvent such as N-methylpyrrolidone or toluene or water. The resulting mixed solution is applied or pressure-bonded onto a current collector described in detail below and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours to form a mixture layer. is made. Regarding the coating method, for example, it is preferable to apply to any thickness and any shape using means such as roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

As the current collector, a current collecting foil such as an aluminum foil or a copper foil can be used. Aluminum foil is preferable as the current collector for the positive electrode, and copper foil is preferable as the current collector for the negative electrode. The thickness of the current collector is preferably 10 to 30 μm. Moreover, the thickness of the mixture layer is preferably 40 to 150 μm (excluding the thickness of the current collector).

<Non-aqueous electrolyte>
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery according to one aspect of the present invention is not particularly limited, and those generally proposed for use in lithium batteries and the like can be used.
Non-aqueous solvents used in the non-aqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, and chloroethylene carbonate, or their fluorides; cyclic esters such as γ-butyrolactone and γ-valerolactone; and dimethyl carbonate. , diethyl carbonate, chain carbonates such as ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2- Ethers such as dimethoxyethane, 1,4-dibutoxyethane and methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; can be mentioned.

The non-aqueous electrolyte according to this embodiment preferably contains a fluorinated cyclic carbonate as a non-aqueous solvent. Using a non-aqueous electrolyte containing a fluorinated cyclic carbonate as the non-aqueous solvent can suppress an increase in AC resistance after storage. Fluorinated cyclic carbonates include 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate and the like. Among them, 4-fluoroethylene carbonate (FEC) is preferably used because it can suppress battery swelling due to gas generation in the battery.
The content of the fluorinated cyclic carbonate is preferably 3 to 30% by volume in the non-aqueous solvent, more preferably 5 to 25%.

Moreover, it is preferable that a compound having an oxalate group bonded to boron is added to the non-aqueous electrolyte according to the present embodiment. A compound having an oxalate group bonded to boron has the effect of reducing the initial AC resistance, and can improve the output characteristics of a non-aqueous electrolyte secondary battery using a lithium-excess type active material for the positive electrode.

Compounds having boron-bonded oxalate groups include lithium bisoxalateborate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), (3-methyl-2,4-pentanedionato)oxalatoborate (MOAB ) and the like. Chemical structural formulas of compounds having each oxalate group are shown below.

リチウムビスオキサレートボレート（ＬｉＢＯＢ）

Lithium bisoxalate borate (LiBOB)

ジフルオロ（オキサラト）ホウ酸リチウム（ＬｉＤＦＯＢ）

Lithium difluoro(oxalato)borate (LiDFOB)

（３-メチル－２，４-ペンタンジオナト）オキサラトボレート（ＭＯＡＢ）

(3-methyl-2,4-pentanedionato)oxalatoborate (MOAB)

The lower limit of the amount of the compound having an oxalate group bonded to boron is preferably 0.1% by mass or more in order to improve the charge-discharge cycle performance with respect to the mass of the entire constituent components other than the electrolyte salt that constitutes the non-aqueous electrolyte. , more preferably 0.2% by mass or more, and the upper limit is preferably 2.0% by mass or less, more preferably 1.0% by mass or less, in order to reduce the possibility of an increase in resistance.

<Method for measuring initial AC resistance>
In the specification of the present application, the initial AC resistance is measured under the following conditions. The target of the measurement is a factory-shipped non-aqueous electrolyte secondary battery that has undergone liquid injection and initial charge/discharge. Prior to the measurement, the battery was charged and discharged at a current of 0.1 C at 25° C. in a predetermined voltage range, then opened and left for 2 hours or longer. By the above operation, the non-aqueous electrolyte secondary battery is brought into a completely discharged state. The resistance value between the positive and negative terminals is measured using an impedance meter that applies an alternating current (AC) of 1 kHz, and this value is defined as "initial AC resistance (mΩ)". Overcharged or overdischarged non-aqueous electrolyte secondary batteries should not be measured.

<Method for measuring AC resistance after storage>
In this specification, the storage test and measurement of AC resistance after storage are performed under the following conditions. The non-aqueous electrolyte secondary battery is charged to a predetermined voltage at 25° C. and 0.1 C to reach a fully charged state. After that, it is left at 45° C. for 15 days. Next, after performing constant current discharge to a predetermined voltage with a current of 0.2 C, the circuit is opened and left for 2 hours or longer. By the above operation, the non-aqueous electrolyte secondary battery is brought into a completely discharged state. Using an impedance meter that applies an alternating current (AC) of 1 kHz, the resistance value between the positive and negative terminals is measured at 25°C. Overcharged or overdischarged non-aqueous electrolyte secondary batteries should not be measured.

Additives generally used for non-aqueous electrolytes may be added to the non-aqueous electrolyte as long as the effects of the present invention are not impaired. For example, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, o-cyclohexylfluorobenzene Fluorinated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole and 3,5-difluoroanisole Overcharge inhibitors such as vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride, etc. Film-forming agents; ethylene sulfite, propylene sulfite, dimethyl sulfite, propanesultone, propenesultone, butanesultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4′-bis(2,2-dioxo-1,3,2-dioxathiolane, 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2- Dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. alone or in combination of two or more can be added to the non-aqueous electrolyte.
The amount of these additives added to the non-aqueous electrolyte is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0, based on the total constituent components other than the electrolyte salt constituting the non-aqueous electrolyte. .1% by mass or more, more preferably 0.2% by mass or more, and the upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less. The purposes of adding these include improvement of charge/discharge efficiency, suppression of resistance increase, suppression of battery swelling, and improvement of charge/discharge cycle performance.

Electrolyte salts used for the non-aqueous electrolyte include, for example, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr , KClO ₄ , inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K) such as KSCN, LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO2) ₂ , LiN( _CF3SO2 )( _C4F9SO2 ), _{LiC ( CF3SO2} ) _{3 , LiC ( C2F5SO2} ) _{3 , ( CH3} ) _4NBF4 , ₍ CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (nC ₄ H ₉ ) ₄ NClO ₄ , (nC _4H9 )4NI, ( _C2H5 ) _{4N -} maleate, ( _C2H5 ) _{4N -} benzoate, _{( C2H5} ) _{4N -} phthalate, lithium stearylsulfonate, lithium _{octylsulfonate} , Examples include organic ion salts such as lithium dodecylbenzenesulfonate and the like, and these ionic compounds can be used alone or in combination of two or more.

Furthermore, by mixing LiPF ₆ or LiBF ₄ with a lithium salt having a perfluoroalkyl group such as LiN(C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further lowered. Low-temperature characteristics can be further improved, and self-discharge can be suppressed, which is more preferable.

Further, a room-temperature molten salt or an ionic liquid may be used as the non-aqueous electrolyte.

The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol/L to 5 mol/L, more preferably 0.5 mol/L, in order to reliably obtain a non-aqueous electrolyte secondary battery having high battery characteristics. ~2.5 mol/L.

<Separator>
As the separator used in the non-aqueous electrolyte secondary battery according to the present embodiment, it is preferable to use a porous film, a non-woven fabric, or the like, which exhibits excellent high-rate discharge performance, alone or in combination. Examples of materials constituting the separator for non-aqueous electrolyte secondary batteries include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride. - hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer , vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexa Fluoropropylene copolymers, vinylidene fluoride-ethylene-tetrafluoroethylene copolymers, and the like can be mentioned.

The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Moreover, the porosity is preferably 20% by volume or more from the viewpoint of charge-discharge characteristics.

Also, the separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinylpyrrolidone, polyvinylidene fluoride, and the like, and a non-aqueous electrolyte. It is preferable to use the non-aqueous electrolyte in the gel state as described above because it has the effect of preventing liquid leakage.

Furthermore, it is preferable to use a polymer gel in combination with the above-described porous membrane or non-woven fabric as the separator because the liquid retention of the non-aqueous electrolyte is improved. That is, by forming a film in which the surface and the wall surfaces of the micropores of a polyethylene microporous membrane are coated with a solvent-philic polymer having a thickness of several μm or less, and holding a non-aqueous electrolyte in the pores of the film, the solvent-philic The polar polymer gels.

Examples of the solvent-philic polymer include, in addition to polyvinylidene fluoride, a crosslinked polymer of an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a monomer having an isocyanate group, or the like. The monomer can be subjected to a cross-linking reaction using heating, ultraviolet rays (UV) in combination with a radical initiator, or actinic rays such as electron beams (EB).

Other battery components include terminals, an insulating plate, a battery case, and the like, and conventionally used parts may be used as they are.

<Non-aqueous electrolyte secondary battery>
FIG. 4 shows a non-aqueous electrolyte secondary battery according to this embodiment. FIG. 4 is a perspective view of the inside of a container of a rectangular non-aqueous electrolyte secondary battery. A nonaqueous electrolyte secondary battery 1 is assembled by injecting a nonaqueous electrolyte (electrolytic solution) into a battery container 3 in which an electrode group 2 is housed. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material with a separator interposed therebetween. The positive electrode is electrically connected to a positive terminal 4 via a positive lead 4', and the negative electrode is electrically connected to a negative terminal 5 via a negative lead 5'.
The shape of the non-aqueous electrolyte secondary battery according to the present embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries (rectangular batteries), and flat batteries.

A non-aqueous electrolyte secondary battery is generally completed and shipped after charging and discharging multiple times in a factory after injecting an electrolyte and sealing.
In the non ^- aqueous electrolyte secondary battery according to the present embodiment, the potential It is shipped without being charged even once until the end of the charging process in which a flat region of change is observed.

The fact that the non-aqueous electrolyte secondary battery according to the present embodiment does not have a history of being charged until the charging process in which the flat region is observed is completed is because the positive electrode active material of the battery is the CuKα A diffraction peak is observed in the range of 20 to 22° in an X-ray diffractogram using a ray, or the battery was charged to a positive electrode potential of 5.0 V (vs. Li/Li ⁺ ). At this time, it can be confirmed by observing a region where the potential change is flat with respect to the amount of charge in the positive electrode potential range of 4.5 to 5.0 V (vs. Li/Li ⁺ ). The details of these confirmation methods are as described above.

The non-aqueous electrolyte secondary battery of this embodiment can also be realized as a power storage device in which a plurality of batteries are assembled. An example of a power storage device is shown in FIG. In FIG. 5 , the power storage device 30 includes a plurality of power storage units 20 . Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1 . The power storage device 30 can be mounted as a power supply for automobiles such as electric vehicles (EV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV).

(Example 1)
<Preparation of lithium transition metal composite oxide>
284 g of nickel sulfate hexahydrate, 303 g of cobalt sulfate heptahydrate, and 443 g of manganese sulfate pentahydrate were weighed and dissolved in 4 L of ion-exchanged water to obtain a Ni:Co:Mn molar ratio of 27: A 1.0 M sulfate aqueous solution of 27:46 was made.
Next, 2 L of ion-exchanged water was poured into a 5-L reactor, and oxygen contained in the ion-exchanged water was removed by bubbling argon gas for 30 minutes. The temperature of the reaction tank was set to 50°C (±2°C), and the inside of the reaction tank was stirred at a rotational speed of 1500 rpm using a paddle blade equipped with a stirring motor. did. The aqueous sulfate solution was added dropwise to the reactor at a rate of 3 mL/min. Here, from the start to the end of dropping, by appropriately dropping a mixed alkaline aqueous solution consisting of 4.0 M sodium hydroxide, 0.5 M ammonia, and 0.2 M hydrazine, the pH in the reaction vessel is The total amount of the reaction solution was controlled so as not to exceed 2 L at all times by controlling to keep the value at 9.8 (±0.1) and discharging a part of the reaction solution by overflow. After the dropwise addition was completed, stirring in the reactor was continued for an additional 3 hours. After stopping the stirring, the mixture was allowed to stand at room temperature for 12 hours or more.
Next, using a suction filtration device, the hydroxide precursor particles produced in the reaction vessel are separated, and furthermore, ion-exchanged water is used to wash and remove sodium ions adhering to the particles, followed by an electric furnace. and dried at 80° C. for 20 hours in an air atmosphere under normal pressure. After that, it was pulverized for several minutes in an automatic mortar made of agate in order to make the particle size uniform. Thus, a hydroxide precursor was produced.
To 1.852 g of the hydroxide precursor, 0.971 g of lithium hydroxide monohydrate was added and mixed well using an agate automatic mortar to obtain a Li:(Ni, Co, Mn) molar ratio of 130: Mixed powder was prepared so that it would be 100. Using a pellet molding machine, it was molded at a pressure of 6 MPa to obtain pellets with a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product would be 2 g. One of the pellets is placed on an alumina boat with a total length of about 100 mm, placed in a box-shaped electric furnace (model number: AMF20), and heated from room temperature to 900 ° C. over 10 hours in an air atmosphere under normal pressure, It was calcined at 900° C. for 5 hours. The internal dimensions of the box-shaped electric furnace are 10 cm long, 20 cm wide and 30 cm deep, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the electric furnace was turned off, and the alumina boat was allowed to cool naturally while left in the furnace. As a result, the temperature of the furnace drops to about 200° C. after 5 hours, but the rate of temperature drop after that is rather slow. After a day and night, after confirming that the temperature of the furnace was 100° C. or lower, the pellets were taken out and lightly pulverized in an agate mortar to make the particle sizes uniform.
Thus _, a lithium transition metal composite _{oxide Li1.13Ni0.235Co0.235Mn0.40O2 was produced} .

<Confirmation of crystal structure>
The lithium transition metal composite oxide was subjected to powder X-ray diffraction measurement using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II), and was confirmed to have an α-NaFeO ₂ type crystal structure.

<Preparation of positive electrode>
Using N-methylpyrrolidone as a dispersion medium, using the lithium transition metal composite oxide (hereinafter referred to as “LR”) as an active material, and using an active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) at a mass ratio of 90: A positive electrode paste for coating was prepared by kneading and dispersing at a ratio of 5:5. The positive electrode paste for coating was applied to one side of a 20 μm-thick aluminum foil current collector, dried and then pressed to prepare a positive electrode according to Example 1.

<Production of negative electrode>
A negative electrode was prepared by placing a metallic lithium foil on a nickel current collector. The amount of lithium metal was adjusted so that the capacity of the battery when combined with the positive electrode was not limited by the negative electrode.

<Assembly of Nonaqueous Electrolyte Secondary Battery>
Using the positive electrode according to Example 1, a non-aqueous electrolyte secondary battery was assembled according to the following procedure.
LiPF ₆ was dissolved in a mixed solvent of 4-fluoroethylene carbonate (FEC)/propylene carbonate (PC)/ethyl methyl carbonate (EMC) at a volume ratio of 1:1:8 to a concentration of 1 mol/L. Lithium difluorophosphate (LiDFP) 0.5% by mass and 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane) (compound A) 1 mass as additives with respect to 100% by mass of the solution % was added as a non-aqueous electrolyte.
A polypropylene microporous membrane surface-modified with polyacrylate was used as a separator. A metal-resin composite film composed of polyethylene terephthalate (15 μm)/aluminum foil (50 μm)/metal-adhesive polypropylene film (50 μm) was used for the exterior body. The positive electrode and the negative electrode according to Example 1 are housed in the exterior body through the separator so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside, and the metal-adhesive polypropylene of the metal-resin composite film The fusion margin where the faces face each other was airtightly sealed except for the portion to be the injection hole, and after the non-aqueous electrolyte was injected, the injection hole was sealed to assemble a non-aqueous electrolyte secondary battery. .

<Initial charge/discharge process>
The assembled non-aqueous electrolyte secondary battery was subjected to an initial charging/discharging process at 25°C. The charging was constant current constant voltage (CCCV) charging with a current of 0.1 C and a final voltage of 4.25 V, and the charging termination condition was the time when the current value was attenuated to 1/6. The discharge was constant current discharge with a current of 0.1C and a final voltage of 2.0V. This charge/discharge was performed twice. Here, a pause step of 30 minutes was provided after charging and after discharging. When the negative electrode material is metallic lithium, the positive electrode potential and the battery voltage are approximately the same value, so the positive electrode potential in the following procedure can be read as the battery voltage of the test battery. It is known that when the counter electrode is graphite, the potential of the positive electrode is obtained by adding the potential of graphite to the battery voltage and adding about 0.1 V.
A non-aqueous electrolyte secondary battery according to Example 1 was completed through the above manufacturing steps.

(Comparative example 1)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that commercially available LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (hereinafter referred to as “NCM523”) was used as the positive electrode active material. Assembly and initial charge/discharge were performed, and a non-aqueous electrolyte secondary battery according to Comparative Example 1 was completed.

(Comparative example 2)
A non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1, except that only the first charge in the initial charge and discharge process was constant current constant voltage (CCCV) charge with a final voltage of 4.6 V. A non-aqueous electrolyte secondary battery according to Comparative Example 2 was completed.

(Example 2)
358 g of the lithium transition metal composite oxide Li _1.13 Ni _0.235 Co _0.235 Mn _0.40 O ₂ prepared in Example 1 was added to 200 mL of a 0.1 M aqueous solution of aluminum sulfate, and stirred using a magnetic stirrer. Stirred at 25° C. and 400 rpm for 30 seconds. Then, it was separated into powder and filtrate by suction filtration. The obtained powder was dried in air at 80° C. for 20 hours. Further, heat treatment was performed in the air at 400° C. for 4 hours using the above-mentioned box-type electric furnace. Thus, a lithium-transition metal composite oxide coated with an aluminum compound (hereinafter referred to as "LR-Al") was produced. The nonaqueous electrolyte secondary battery was assembled and initially charged and discharged in the same manner as in Example 1, except that this lithium transition metal composite oxide was used as the positive electrode active material. Finished the battery.

<Confirmation of X-ray diffraction peak of positive electrode active material>
X-ray diffraction measurement was performed under the conditions described above using the positive electrode mixtures collected from the non-aqueous electrolyte secondary batteries after the initial charge/discharge according to Example 1 and Comparative Example 2 according to the procedures and conditions described above. In the positive electrode active material of Example 1, a diffraction peak is observed in the range of 20 to 22° in the X-ray diffraction diagram using CuKα rays (see the lower part of FIG. 1). confirmed that no diffraction peak was observed in the range of 20 to 22° (see upper part of Fig. 1).

<Overcharge test>
Using the non-aqueous electrolyte secondary batteries according to Examples and Comparative Examples, constant current (CC) charging was performed at a current value of 10 mA per 1 g of positive electrode mixture without setting an upper limit for battery voltage. This charge corresponds to the third charge including the initial charge/discharge. Here, when the capacity when reaching 4.45 V (vs. Li/Li ⁺ ) from the start of charging is X (mAh), and the capacity at each voltage is Y (mAh), Y/X*100 is the capacity ratio Z (%), and the capacity ratio Z (%) when the positive electrode potential rapidly increased and reached 5.1 V (vs. Li/Li ⁺ ) was recorded as the “retarding effect”. Also, the maximum value of dZ/dV was obtained.

Table 1 shows the delay effect (%) and the maximum value of dZ/dV in the overcharge test of the non-aqueous electrolyte secondary batteries according to Examples 1 and 2 and Comparative Examples 1 and 2.

According to Table 1, in the overcharge test, the positive electrode potential of the non-aqueous electrolyte secondary battery according to Comparative Example 1, which has a positive electrode using NCM523, rapidly increased to 5.1 V (vs. Li/ Li ⁺ ), and the retardation effect is not sufficient. This is because in the overcharge test, when charging was performed without setting the upper limit of the voltage, the positive electrode of the non-aqueous electrolyte secondary battery according to Comparative Example 1 was 4.5 to 5.0 V (vs. Li/Li ⁺ ) within the range of positive electrode potential (maximum value of dZ/dV is less than 150).
In addition, the non-aqueous electrolyte secondary battery according to Comparative Example 2 has a positive electrode using a lithium-excess active material. Again, the delay effect is not sufficient. This is because the positive electrode potential was charged to 4.6 V (vs. Li/Li ⁺ ) in the initial charge/discharge process, so in the overcharge test, when charging was performed without setting the upper limit of the voltage, the comparison In the positive electrode of the non-aqueous electrolyte secondary battery according to Example 2, a region where the potential change is flat with respect to the amount of charged electricity is observed within the positive electrode potential range of 4.5 to 5.0 V (vs. Li/Li ⁺ ). (maximum dZ/dV less than 150).
On the other hand, the non-aqueous electrolytes according to Examples 1 and 2 were provided with a positive electrode using a lithium-excess active material, and the initial charge/discharge process was performed at a potential of less than 4.5 V (vs. Li/Li ⁺ ). In the following batteries, an excellent delay effect as compared with Comparative Examples 1 and 2 is observed. This is because the positive electrode of the non-aqueous electrolyte secondary batteries according to Examples 1 and 2 is within the positive electrode potential range of 4.5 to 5.0 V (vs. Li/Li ⁺ ). is associated with the observation of a flat region (maximum value of dZ/dV greater than or equal to 150).

Next, a non-aqueous electrolyte battery was produced in which the composition of the non-aqueous electrolyte was changed from that of Example 1 or 2.

(Example 3)
In the same manner as in Example 1, except that the solvent for the non-aqueous electrolyte was changed to a mixed solvent of ethylene carbonate (EC)/propylene carbonate (PC)/ethyl methyl carbonate (EMC) with a volume ratio of 25:5:70. , the non-aqueous electrolyte secondary battery was assembled and the initial charge and discharge were performed to complete the non-aqueous electrolyte secondary battery according to Example 3.

(Example 4)
In the same manner as in Example 1, except that the solvent for the non-aqueous electrolyte was changed in the same manner as in Example 3, and 0.2% by mass of vinylene carbonate (VC) was added as an additive to the mass of the non-aqueous electrolyte. , the non-aqueous electrolyte secondary battery was assembled and the initial charge and discharge were performed to complete the non-aqueous electrolyte secondary battery according to Example 4.

(Example 5)
Assembly and initial charge/discharge of a non-aqueous electrolyte secondary battery were performed in the same manner as in Example 1, except that the solvent of the non-aqueous electrolyte was changed to a mixed solvent having a volume ratio of FEC/EMC of 20:80. A non-aqueous electrolyte secondary battery according to Example 5 was completed.

(Example 6)
Assembly and initial charge/discharge of a non-aqueous electrolyte secondary battery were performed in the same manner as in Example 1, except that the solvent of the non-aqueous electrolyte was changed to a mixed solvent having an FEC/EMC volume ratio of 5:95. A non-aqueous electrolyte secondary battery according to Example 6 was completed.

(Examples 7 and 8)
A nonaqueous electrolyte secondary battery was prepared in the same manner as in Examples 3 and 4, respectively, except that the positive electrode active material was changed to the lithium transition metal composite oxide (LR-Al) coated with the aluminum compound prepared in Example 2. and initial charge/discharge were performed to complete the non-aqueous electrolyte secondary batteries according to Examples 7 and 8.

<Storage test>
The initial AC resistance of the non-aqueous electrolyte secondary batteries according to Examples 1 to 8 was measured under the conditions described above. After that, a storage test was performed under the conditions described above, and the AC resistance after storage was measured. The rate of increase (%) in the AC resistance after storage relative to the initial AC resistance was defined as the "rate of increase in resistance on the 15th day relative to the initial stage." Table 2 shows the resistance increase rate (%) of the non-aqueous electrolyte secondary batteries according to Examples 1 to 8 on the 15th day compared to the initial stage.

According to Table 2, in Examples 1 and 3 to 6 using LR as the positive electrode active material, compared with the non-aqueous electrolyte secondary batteries according to Examples 3 and 4 using non-aqueous electrolytes containing no FEC, FEC In the non-aqueous electrolyte secondary batteries according to Examples 1, 5, and 6 using the non-aqueous electrolyte containing, it can be seen that the increase in AC resistance after storage is further suppressed. In addition, in Examples 2, 7, and 8 using LR-Al as the positive electrode active material, compared to the non-aqueous electrolyte secondary batteries according to Examples 7 and 8 using a non-aqueous electrolyte that does not contain FEC, In the non-aqueous electrolyte secondary battery according to Example 2 using the non-aqueous electrolyte containing FEC, it can be seen that the increase in AC resistance after storage is further suppressed.

Next, an example in which the additive of the non-aqueous electrolyte is changed is shown.
(Example 9)
100 mass of a solution in which LiPF ₆ was dissolved to a concentration of 1 mol/L in a mixed solvent of ethylene carbonate (EC)/propylene carbonate (PC)/ethyl methyl carbonate (EMC) at a volume ratio of 25:5:70. %, 1.0% by mass of compound A alone was added as an additive to the non-aqueous electrolyte.
Coating using graphite as a negative electrode active material, containing graphite: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) at a mass ratio of 97: 2: 1 (in terms of solid content), and using water as a solvent A negative electrode paste was prepared, applied to one side of a strip-shaped copper foil current collector having a thickness of 10 μm, and dried. After pressurizing this with a roller press, it was dried under reduced pressure at 100° C. for 12 hours to remove moisture in the electrode plate. Thus, a negative electrode was produced.
A non-aqueous electrolyte secondary battery according to Example 9 was completed by assembling the non-aqueous electrolyte secondary battery and performing initial charging and discharging in the same manner as in Example 3 except that the non-aqueous electrolyte and the negative electrode were used. In addition, when the first and second charges in the initial charge and discharge process are constant current and constant voltage (CCCV) charges with a final voltage of 4.25 V, the potential of the graphite negative electrode in a fully charged state is 0.1 V (vs. Li / Li ⁺ ), and the positive electrode potential reaches about 4.35 V (vs. Li/Li ⁺ ).

(Examples 10-12)
except that LiDFOB was added at 0.2, 0.5, and 1.0 wt. Non-aqueous electrolyte secondary batteries according to Examples 10 to 12 were completed in the same manner as in Example 9.

(Examples 13 and 14)
Non-aqueous electrolyte secondary batteries according to Examples 13 and 14 were produced in the same manner as in Example 11, except that LiBOB and MOAB were used as additives instead of LiDFOB.

(Comparative Examples 3-6)
Comparative Example 3 in the same manner as in Examples 9, 11, 13 and 14, respectively, except that in the initial charge and discharge step, the first and second charges were constant current constant voltage (CCCV) charge with a final voltage of 4.5 V. Non-aqueous electrolyte secondary batteries according to 6 were produced. The potential of the graphite negative electrode in the fully charged state in the initial charge/discharge step is about 0.1 V (vs. Li/Li ⁺ ), and the positive electrode potential reaches about 4.6 V (vs. Li/Li ⁺ ). there is

The initial AC resistance of the nonaqueous electrolyte secondary batteries of Examples 9 to 14 and Comparative Examples 3 to 6 was measured, and when the compound having an oxalate group bonded to boron was not contained as an additive (Example 9 and Comparative The change rate of the initial AC resistance of the non-aqueous electrolyte secondary battery containing the additive with respect to the initial AC resistance of the non-aqueous electrolyte secondary battery according to Example 3) was obtained as "resistance change rate/%". The results are shown in Table 3 below. The "addition amount/mass%" in Table 3 is "mass percent of the addition amount of the compound having an oxalate group bonded to boron".

According to Table 3, the non-aqueous electrolytes according to Examples 9 to 14 were produced using LR as the positive electrode active material and setting the maximum potential of the positive electrode to less than 4.5 V (vs. Li/Li ⁺ ) in the initial charge/discharge process. The secondary battery has a higher initial AC resistance than the non-aqueous electrolyte secondary batteries according to Comparative Examples 3 to 6, which were initially charged and discharged so that the maximum potential of the positive electrode reached 4.5 V (vs. Li/Li ⁺ ) or more. is reduced. The maximum attainable potential of the positive electrode of the non-aqueous electrolyte secondary batteries of Comparative Examples 3 to 6 is about 4.6 V (vs. Li/Li ⁺ ) as described above. Among the examples, Examples 10 to 14, in which the non-aqueous electrolyte contained, as an additive, a compound having an oxalate group bonded to boron, further improved the initial AC resistance compared to Example 9 in which the compound was not included. It turns out that there exists an effect to reduce.
In the non-aqueous electrolyte secondary batteries according to Comparative Examples 3 to 6, in which the same LR as in Examples 9 to 14 was used as the positive electrode active material for the positive electrode, the maximum potential of the positive electrode in the initial charge and discharge process was 4.5 V (vs. Li /Li ⁺ ) or more. Therefore, it is confirmed that the diffraction peak in the range of 20 to 22° of the positive electrode active material has disappeared by the method of confirming the diffraction peak according to the procedure described above. . The non-aqueous electrolyte secondary batteries according to the comparative examples all have higher initial AC resistance than the non-aqueous electrolyte secondary batteries according to Examples 9 to 14, and the non-aqueous electrolyte binds to boron. Since the initial AC resistance is further increased by including the compound having an oxalate group as an additive, it can be seen that the inclusion of said compound has the opposite effect of reducing the initial AC resistance.

Even when the non-aqueous electrolyte secondary battery according to the present invention is accidentally overcharged, no rapid increase in battery voltage is observed up to a higher SOC.
Further, by including the fluorinated cyclic carbonate in the non-aqueous solvent of the non-aqueous electrolyte, it is possible to suppress an increase in AC resistance after storage.
Furthermore, the initial AC resistance can be reduced by including a compound having an oxalate group bonded to boron in the non-aqueous electrolyte.
Therefore, the non-aqueous electrolyte secondary battery according to the present invention can be used as a battery for hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and electric vehicles (EV) that require high safety and storage performance. Highly useful.

1 non-aqueous electrolyte secondary battery 2 electrode group 3 battery container 4 positive electrode terminal 4' positive electrode lead 5 negative electrode terminal 5' negative electrode lead 20 power storage unit 30 power storage device

Claims (7)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte,
The positive electrode, as an active material,
α-NaFeO ₂ type crystal structure,
Represented by the general formula Li _1+α Me _1-α O ₂ (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co), and the molar ratio of Li to the transition metal (Me) is 1 .15<Li/Me comprising a lithium transition metal composite oxide,
The active material has a diffraction peak in the range of 20 to 22° in an X-ray diffraction diagram using CuKα rays ,
A non-aqueous electrolyte secondary battery , wherein the non-aqueous electrolyte contains a fluorinated cyclic carbonate in a non-aqueous solvent . A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte,
The positive electrode, as an active material,
α-NaFeO ₂ type crystal structure,
Represented by the general formula Li _1+α Me _1-α O ₂ (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co), and the molar ratio of Li to the transition metal (Me) is 1 .15<Li/Me comprising a lithium transition metal composite oxide,
When the positive electrode is charged to a positive electrode potential of 5.0 V (vs. Li/Li ⁺ ), the positive electrode potential is within the positive electrode potential range of 4.5 to 5.0 V (vs. Li/Li ⁺ ). A relatively flat region of potential change is observed with respect to the amount of
A non-aqueous electrolyte secondary battery , wherein the non-aqueous electrolyte contains a fluorinated cyclic carbonate in a non-aqueous solvent . 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide contained as an active material in the positive electrode has a molar ratio of Mn to transition metal (Me) of 0.4≦Mn/Me. . The lithium-transition metal composite oxide contained as an active material in the positive electrode has a molar ratio of Li to transition metal ( Me) of Li/Me ≤ 1.35. Water electrolyte secondary battery. The non-aqueous battery according to any one of claims 1 to 4 , which is used at a battery voltage where the maximum potential of the positive electrode in a fully charged state (SOC 100%) is less than 4.5 V (vs. Li/Li ⁺ ). Electrolyte secondary battery. 6. The non-aqueous electrolyte secondary battery according to claim 1 , wherein said non-aqueous electrolyte contains a compound having an oxalate group bonded to boron. The method for manufacturing the non-aqueous electrolyte secondary battery according to any one of claims 1 to 6 , wherein the maximum potential of the positive electrode in the initial charge and discharge process is less than 4.5 V (vs. Li/Li ⁺ ). A method for manufacturing a non-aqueous electrolyte secondary battery.

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